We put up with too many cables. There are at least four different kinds of USB plugs, two kinds of FireWire and like a million different ways to connect something to TV or monitor. Modern gadget life can be kind of retarded in this way. Why not one kind of cable, or just a couple? I don't know. But until everyone gets on the same appendage-to-hole scheme, in the meantime, you can use this: an illustrated guide to pretty much every kind of cable you will see in current gadgets and what it's used for (unless, you know, Sony springs a new one on us overnight, which is honestly possible).
Click to viewUSB Type A Universal Serial Bus, the gold standard. The whole idea behind it is that this one interface will connect everything (except the stuff it doesn't), killing off the old guard, like parallel and serial ports. It moves data, and in the case of USB 2.0-which is pretty much the standard now-it does it faster, and with some extra specs for power. Clarification: USB 2.0 adds in the Battery Charging specification 1.0, which allows for dedicated charging and other power goodness. This particular connector is the type A variety. It plugs everything from your iPod to your digital camera into a computer, or whatever else. If you haven't seen this before, what are you reading this on?
USB Type B The USB Type B plug is basically a USB connector for peripherals-you've probably seen it jacked into a printer or scanner.
Mini USB It's a type of USB connector for smaller devices like cameras and phones-it takes up less real estate than a port for a Type A connection, obviously.
Micro USB Even smaller than the above Mini USB. Since it's, like, even smaller, we're starting to see it adopted by LG, Motorola and others-hopefully this is the last time they all switch power adapters on us, till wireless power makes adapters unnecessary. Update: Better pic via Mobile Burn.
IEEE 1394 (aka FireWire) An alternative to USB, Apple popularized the IEEE 1394 interface as FireWire (Sony called it i.LINK). You're probably most familiar with it on a digital camcorder (or an old school iPod), since it's really speedy for data transfers. You're looking at the four- and six-pin versions of FireWire 400. The six-pin version delivers power, the four-pin version (originally favored by Sony) doesn't.
RJ45 The kind of plug you're used to seeing on the end of a Category 5, Cat5 enhanced or Cat6 (commonly known as Ethernet) cable, which is plugged into your router or computer's networking port. Cat5e is an update to Cat5 that supports faster Gigabit Ethernet. Cat6 is the next-gen standard that will handle speeds twice as fast as Cat5e, and has stricter rules about noise and crosstalk. Interestingly, the most recently approved IEEE 1394 spec (aka FireWire S800T) uses RJ45 connectors as well.
eSATA External Serial ATA is a branch off of the Serial ATA interface that connects your hard drive to your computer if it was put together in the last couple of years. As you can guess from the name, the difference is it's an external port, but it delivers the same insane data transfer speeds as the hookup to your hard drive. Faster than USB or FireWire, it's basically for external hard drives for quicker data transfers. You'll be seeing it more as more laptops include a port for it, usually one that can also be used with USB. There's even talk of bus-powered eSATA coming in the next year or two.
HDMI High-Definition Multimedia Interface is another one of those "it'll connect everything except all the stuff it doesn't" deals, but for high-definition audio and video. It basically replaces DVI (see below) plus S-Video and all that other analog crap. Laptops, desktops and even high-end cameras and other gadgets are getting HDMI. Besides fat bandwidth, another benefit is control: The Consumer Electronics Control (CEC) profile already lets machines send commands to other products over HDMI-that or something like it could be very useful in the PC space, too.
DVI The digital successor to VGA, Digital Visual Interface is a video connection you'll most likely see dealing with computers or computer monitors, at least until they're all replaced by HDMI. Older HDTVs have DVI ports too. It can have a few different pin arrangements, depending on whether it carries a digital (DVI-D) or analog (DVI-A) signal or both (DVI-I, for integrated). The analog deal on some types is to make them easy to adapt for use with a VGA monitor, but it's less and less noteworthy. There's also a dual-link version that carries more data for high-res displays. These are helpfully depicted at Wikipedia.
Mini and Micro DVI are dumb, shrunken, Apple-only versions of DVI. Why dumb? Because they're essentially proprietary formats. HDMI will make them obsolete before long.
DisplayPort is the newest video interface on the block, and its plane of existence is basically in the computer-to-monitor realm only. It's not even close to mainstream yet, but Dell is backing it, among others, so you might wanna know it. It can carry a whole lot of data, but it's got DRM built into the spec, so it's a double-edged sword. Update: Swapped pic out with a better one.